1. Field
Example embodiments include compositions useful in forming patterns from active layers during fabrication of memory devices, methods of forming active patterns using such compositions, and organic semiconductor devices incorporating such active patterns. More particularly, example embodiments include compositions which are based on one or more N-containing conjugated electroconductive polymers and at least one photoacid generator that can be patterned without using a separate photoresist pattern, methods of forming such patterns using such compositions, and organic memory devices comprising such an active pattern.
2. Description of the Related Art
With the recent impressive advances in the information and communication industry, demand for various types of solid state memory devices have been increasing. Particularly, portable terminals, versatile smart cards, electronic money, digital cameras, gaming devices, and MP3 players require non-volatile memory devices, e.g., memory devices capable of retaining data once the power is switched off. Prevalent among non-volatile memories are flash memories that are based on silicon materials.
Conventional flash memories are restricted in the number of times that they can be erased and re-programmed, and tend to have relatively slow recording rates. Further, the memory capacity of such devices in predicated on large scale integration which requires the formation of increasingly fine structures, giving rise to increased production costs and/or complicated processing. Additionally, conventional flash memories are approaching limits beyond which further miniaturization of the device structures will reach physical and/or technical limitations.
As conventional flash memory devices reach these technical limitations, ongoing research and development efforts have been directed to the identification, development and/or refinement of next-generation non-volatile memories. These next-generation non-volatile memories are expected to provide advantages over the conventional flash memory devices including, for example, increased speed, reduced power consumption, increased capacity and/or reduced cost.
Depending on the material constituting the cell, next-generation memories receiving particular attention include those that may be classified as ferroelectric RAM, magnetic RAM, phase change RAM, nanotube memory, holographic memory and organic memory. Of these devices, the organic memory devices, which feature the use of an organic material formed between two electrodes with a voltage applied thereto, operate on the principle of electrical bistability, a phenomenon in which a material exhibits two distinct states of conductivity at the same applied voltage that can be utilized to form a memory cell. That is, the organic memory devices include memory cells that are capable of supporting the reading and writing of data values corresponding to a “0” and a “1” by altering the resistance of the organic material between the two electrodes in response to electrical signals of sufficient polarity and magnitude. As a result of these properties, organic memory devices are expected to overcome certain of the problems associated with conventional flash memories and exhibit, for example, improved processability, reduced production costs and/or increased degrees of integration while still maintaining the non-volatility memory characteristics.
An organic memory cell, as illustrated in FIG. 1, typically comprises a lower electrode 10 and an upper electrode 30 with an organic active layer 20 interposed therebetween. Typically, a memory device includes a large array of such memory cells and certain peripheral circuitry for selectively addressing certain of the memory cells for writing data to and reading data from the accessed memory cells. In order to form such memory cell arrays, the organic active layer and the layers of electrode material need be patterned to define the individual memory cells.
Most conventional patterning methods employ heat or an e-beam for depositing a shadow mask even when the active layer consists of monomers, or comprise selective exposure/etching steps utilizing a separately formed photoresist pattern to form an active pattern. For example, a layer of an electroconductive material is formed across the surface of a substrate to form a lower electrode. This layer of electroconductive material is then coated with a photoresist composition containing an organic active material, portions of the photoresist composition are exposed to form an exposed photoresist layer. The exposed photoresist layer is then developed to remove portions of the photoresist layer, thereby forming a photoresist pattern that can, in turn, be used as an etch mask for removing exposed portions of the organic active layer and the electroconductive layer to form an active pattern. These conventional photoresist techniques, however, are relatively complicated and tend to increase the production costs due, in part, to the use of expensive apparatus.
Conventional conjugated polymers are typically patterned using, for example, soft lithography or ink jetting, but such techniques are not generally suited for production of highly integrated memory devices. Soft lithography takes advantage of a mechanism in which the active layer is cured with heat or light, but the range of materials that can be used in such a process is relatively limited. Ink jet technologies as well tend to be generally suitable for less demanding device pattern requirements, by have proven generally unsuitable for forming patterns having critical dimensions (CD) below a microns using currently available technology. Additional difficulties with conventional ink jet technologies have been associated with the selection of proper solvents and the ability to control and maintain concentrations to a degree sufficient to maintain the desired feature sizing.